Aluminum-casting grain refinement

ABSTRACT

This invention teaches a method of controlling the size of the grain structure in aluminum and aluminum-based alloys employing as the novel grain-refining addition silver oxide. The added silver oxide promptly reacts with the molten aluminum to produce silver which dissolves in the aluminum and freshly precipitated and very active aluminum oxide which acts as a potent grainrefining agent.

United States Patent [72] Inventors 211 Appl. No.

[22] Filed [45] Patented [73] Assignee Gustaf F. Bolling Dearborn;

Jean Cisse, Dearborn Heights; Gerald S.

Cole, Dearborn, all of, Mich. 839,474

July 7, l969 Sept. 21, 1971 Ford Motor Company Dearborn, Mich.

[56] References Cited UNITED STATES PATENTS 3,355,281 11/1967 Hansley eta1. 75/138 OTHER REFERENCES Orehoski, Improved Crystal Structure in CastSteel lngots, Journal of Metals, May, 1969, Pages 41- 48. Copy inScientific Library of Patent Office.

Primary ExaminerRichard 0. Dean ALUMINUM-CASTING GRAIN HISTORICALLY Thisinvention should be considered in view of the teachings of applicationSer. No. 760,126, filed Sept. 13, 1968, and-a more recent applicationSer. No. 833,446, filed June 16, 1969. Both of these applications arefiled in the names of G. F. Bolling and G. S. Cole and are assigned tothe assignee of this invention.

These previously filed applications teach the control of grain structureparticularly in castings which are approximate objects of revolution,either by slow rotation or very mild angular acceleration, about an axispreferably coincident with the axis of the casting. The speed ofrotation or angular oscillation treated in all of these inventions isonly of the order of 60 r.p.m. and is by no means to be confused withthe much higher rates of rotation employed in conventional centrifugalcastings.

The earlier applications mentioned above described in detail the castingof uninoculated INCO 713 turbine wheels. The only inoculation taught bythese earlier applications is a minor inoculant coating of the mold asopposed to the present invention in which the inoculant is incorporateddirectly into metal whose solidification characteristics are to becontrolled.

THE INVENTION This invention is related to the subject matter of both ofthe above-mentioned applications and particularly to the later filedapplication relating to the addition of an inoculant directly to themetal whose solidification characteristics are to be controlled. Thislater filed application teaches that the addition of an inoculant to acasting which is to be subject to slow rotation or oscillation duringcooling directly reverses the results obtained with uninoculatedcastings. In theuninoculated castings steady-state rotation produces acolumnar struc was 1 percent.

minum silver alloy also containing 6.4 percent silver. This alloydiffers from that of FIG. 1 in that the silver was produced in situ bythe addition of silver oxide to the melt. This initiated thetypical-thermit reaction and produced silver and freshly precipitatedaluminum oxide. The aluminum oxide content FIG. 3 depicts the structureof an ingot containing 1.28 percent silver. This silver content of thealloy was also produced by the thermit reaction by the addition ofsilver oxide to the melt. This resulted in the concomitant production of0.2 percent of freshly precipitated aluminum oxide.

The metallurgical structure depicted in FIG. 1 is that of gross columnargrains which one would normally anticipate upon the undisturbed coolingof an aluminum ingot in the uninoculated condition. The presence of 6.4percent silver did not change the anticipated grain structure.

The structure depicted in FIG. 2 is an alloy of similar composition, butmodified by the addition of the aluminum oxide in the freshlyprecipitated and very active form resulting from the oxidation ofaluminum by added silver oxide which in turn is reduced to producemetallic silver. This addition considerably refined the structure andadded a tendency to be partially equiaxed instead of completelycolumnar.

The structure shown in FIG. 3 shows the potent grain refining action ofas little as 0.2 percent aluminum oxide which has been freshlyprecipitated in the melt. This melt was prepared by the addition to themelt of silver oxide sufficient to produce a silver content of 1.28percent. The added silver oxide quickly reacted with the aluminum by thethermit reaction to produce metallic silver and a very active form offreshly precipitated aluminum oxide. In this particular ingot the normalgrain refining action of the freshly precipitated aluminum oxide in theareas near the surface has been overpowered by the fact that this ingotwas subject to angular accelerations during solidification. However, asthe center of the ingot it approached the effect of these angularaccelerations became negligible due to the small radius of gyration. Inthis inner area the very fine-grained structure produced by the freshlyprecipitated aluminum oxide in the undisturbed metal is very apparent.

We claim as our invention:

1. The process of refining the grain structure in an aluminum basecasting comprising adding to the molten metal silver oxide, permittingthesilver oxide to react with the molten metal to produce silver whichalloys with the molten metal and freshly precipitated and very activealuminum oxide which acts as an effective aluminum grain-refining agent.

